FreeBSD Security Advisory (FreeBSD-SA-06:17.sendmail.asc)

The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-06:17.sendmail.asc
Upgrade your system to the appropriate stable release or security branch dated after the correction date
FreeBSD includes sendmail(8), a general purpose internetwork mail routing facility, as the default Mail Transfer Agent (MTA). A suitably malformed multipart MIME message can cause sendmail to exceed predefined limits on its stack usage.